Add a marker for retpoline to the module VERMAGIC. This catches the casewhen a non RETPOLINE compiled module gets loaded into a retpoline kernel,making it insecure.

It doesn't handle the case when retpoline has been runtime disabled. Evenin this case the match of the retcompile status will be enforced. Thisimplies that even with retpoline run time disabled all modules loaded needto be recompiled.